OpinionPhaseSeparationandtheCentrosome:AFaitAccompli?JordanW.Raff1,*Thereiscurrentlyintenseinterestintheideathatmanymembranelessorganellesmightassemblethroughphaseseparationoftheirconstituentmoleculesintobiomolecular'condensates'thathaveliquid-likeproperties.Thisideaisintu-itivelyappealing,especiallyforcomplexorganellessuchascentrosomes,wherealiquid-likestructurewouldallowthemanyconstituentmoleculestodiffuseandinteractwithoneanotherefficiently.Idiscusshererecentstudiesthateithersupporttheconceptofaliquid-likecentrosomeorsuggestthatcentrosomesareassembleduponamoresolid,stablescaffold.Isuggestthatitmaybedifficulttodistinguishbetweenthesepossibilities.Iarguethattheconceptofbiomolecularcondensatesisanimportantadvanceincellbiology,withpotentiallywide-rangingimplications,butitseemsprematuretoconcludethatcentrosomes,andperhapsothermembranelessorganelles,arenecessarilybestdescribedasliquid-likephase-separatedcondensates.TheCellBiologyofLiquid–LiquidPhaseSeparation(LLPS)Incellbiology,therehasbeengreatinterestrecentlyintheideathatmanymembranelessorgan-ellesmaybeformedbyphaseseparationoftheirconstituentmoleculesintodroplets–morerecentlytermedbiomolecular'condensates'–thathavegel-orliquid-likeproperties[1].Theassemblyofthesecondensatesisusuallydrivenbyproteins,ofteninassociationwithnucleicacids,thathaveintrinsicallydisorderedregions(IDRs)and/orlowcomplexitydomains(LCDs),ormultiplecopiesofdomainsthatinteractwithoneanotherwithrelativelylowaffinity[2,3].Thisemergingfieldhasbeenreviewedextensively[4–7].Althoughmostcellbiologistshaveanintuitiveunderstandingofthedifferencesbetweenasolidandaliquid,fewhavethegroundinginphysicalchemistryorthephysicsofsoftmattertounder-standthenuancesofthesedifferenceswhenappliedtocells.Thephysicsthatdescribesthebehaviourofanidealsolid,liquid,orgasiswellunderstood,butfewcellstructuresbehavelikeanyoftheseidealstates:theyoftenexhibitviscoelasticbehaviours,meaningthatunderdifferentconditionstheycanbemoreliquid-likeormoresolid-like,andtryingtoundersta...
